White Island, New Zealand, is an active andesitic volcano that is located near the southern end of the Tonga-Kermadec Volcanic Arc at the convergent plate boundary where the Pacific Plate is being subducted beneath the Indian-Australian Plate. The plate tectonic setting, volcanic features and the petrology of White Island are thought to be characteristic of the environment associated with formation of porphyry copper deposits. White Island has only been active for about 10 Ka and, as such, is thought to be an ideal location to study early magmatic processes associated with formation of porphyry copper deposits. In this study, the geochemistry of the silicate melt at White Island has been characterized through detailed studies of silicate melt inclusions, phenocrysts, and matrix glass contained in recent ejecta (1977-1991). Most melt inclusions contained only glass, however, daughter minerals present in multiphase melt inclusions in the 1991 sample indicate a different P-T history compared to the other samples. Samples studied are vesicular porphyritic andesitic dacites containing phenocrysts of plagioclase, orthopyroxene, and clinopyroxene. A glassy matrix containing crystallites surrounds the phenocrysts. Both mineral and silicate melt inclusions occur in all three phenocryst phases. Inclusions of plagioclase occur in pyroxenes and inclusions of orthopyroxene and clinopyroxene occur in plagioclase. Compositions of minerals are independent of mode of occurrence - that is, plagioclase (and orthopyroxene and clinopyroxene) compositions are the same regardless of whether they occur as phenocrysts or as inclusions in another mineral. Moreover, compositions of mineral inclusions and phenocrysts show no systematic variation within individual samples or in samples representing different eruptive events, indicating that the magma chamber is chemically homogenous over the time-space scale being sampled. Various major, trace element and volatile compositional features of economic and non-economic (or barren) porphyry copper systems were compared to the White Island data. The Al2O3/(Na2O+K2O+CaO) ratio observed in economic porphyry copper deposits is always greater than or equal to 1.3, and glass in one phase melt inclusions, as well as glass in unhomogenized (1991) inclusions from White Island equal or exceed this value. The glass in the unhomogenized 1991 melt inclusions is corundum normative, with Si/(Si+Ca+Mg+Fet)>0.91, and K/(K+Ca+Mg+Fet)>0.36, all of which are characteristic of productive systems. Melt inclusions from White Island also show a positive Eu anomaly similar to that found in productive porphyry deposits, whereas non-productive systems show a negative Eu anomaly. Copper concentrations (170-230 ppm) in melt inclusions from White Island are sufficiently high to generate an economic porphyry copper deposit based on theoretical models. High Cl/H2O ratios (0.15) in melt inclusions furthermore indicate that copper will be efficiently partitioned from the melt into the magmatic aqueous phase. The inferred pressure in the magma chamber at depth (1 kbar) is ideal for extracting copper from the melt, and mineral phases (pyrrhotite, biotite or amphibole) which could scavenge copper before it could be partitioned into the magmatic vapor phase are absent. Concentrations of S in the melt are also low, which would prevent pyrrhotite from crystallizing. The tectonic setting and geochemical characteristics of the magma body at White Island are similar to features observed in economic porphyry systems elsewhere. These data suggest that development of economic porphyry copper mineralization at White Island is likely. / Master of Science

Northwestern Mexico is characterized by different metallogenic provinces that are included along the Basin and Range, the Sierra Madre Occidental, and the Baja California geological provinces. With the purpose of contribute to the current understanding of the mineralizing processes, the present study focused on two important copper metallogenic provinces: the Cananea Porphyry District in Sonora, and the Sediment-hosted Stratiform Copper- and Mn-deposits in Baja California Sur. The U-Pb zircon ages from the mineralizing porphyries from Cananea district suggest a continued magmatic activity period of ~6 Ma. Also suggests a period of ~20 Ma for the entire magmatic activity in the district. The Re-Os molybdenite ages demonstrate five well-constrained mineralization events in the district; the main mineralization is constrained over a short period of time (~4 Ma). The new molybdenite age from the Pilar deposit documents the oldest mineralizing pulse, suggesting possibly the initiation of the Laramide mineralization in northern Sonora. A detailed study of Mariquita porphyry Cu and Lucy Cu-Mo deposits in the Cananea district was performed. Four hydrothermal stages were defined in Mariquita, whereas a single hydrothermal pulse characterizes Lucy. Emplacement depths between 1-1.2 km, and temperatures between 430-380ºC characterized the mineralization from Mariquita, whereas deeper emplacement depths and higher mineralization temperatures characterized Lucy. The stable isotope systematic and fluid inclusion data determined that the mineralizing fluids in Mariquita deposit are essentially magmatic during the earlier hydrothermal stages, whereas the last stage is the mixing between magmatic and winter meteoric-waters. The mineralizing fluids from Lucy deposit are magmatic in origin. A comprehensive study was performed in the Cu-Co-Zn-Mn ineralization of the Boléo District, and Mn-oxide mineralization along the eastern coast Baja California Sur. The REE and trace element in the Mn-oxides demonstrated the exhalative nature of the mineralizing hydrothermal fluids, and exclude the hydrogenous nature. The stable isotope systematic in ore and gangue minerals, along with the Cu-isotope data helped to decipher the nature of mineralizing and non-mineralizing fluids. The application of Pb, Sr and Re-Os isotope systems was applied to constrain the nature of the fluids involved during the mineralization processes and that the metal sources.

In order to improve our understanding of poorly studied Mexican Porphyry Copper Deposits in the SW regional metallogenetic province, a detailed study of the hydrothermal fluid evolution of La Caridad porphyry copper-molybdenum deposit, and its connection to a high sulfidation epithermal deposit, was performed using oxygen, hydrogen and sulfur stable isotopes combined with fluid inclusion studies. In addition, UPb and Re-Os geochronology from La Caridad, Milpillas and El Arco porphyry deposit were performed to constrain the timing of mineralization and magmatism in northwest Mexico. Uranium-lead zircon ages from La Caridad suggest a short period of magmatism, between 55.5 and 53.0 Ma. Re-Os molybdenite ages from potassic and phyllic hydrothermal veins yielded identical ages within error, 53.6 ± 0.3 Ma and 53.8 ± 0.3 Ma, respectively. Four stages of hypogene alteration and mineralization are recognized at La Caridad porphyry copper deposit. The isotopic composition of the water in equilibrium with hydrothermal alteration minerals is consistent with highly evaporated lacustrine waters mixed with magmatic waters or vapor separated from magmatic fluids, however, sulfur isotopes and fluid inclusions data support the lacustrine-magmatic water hypothesis. Milpillas porphyry copper deposit in the Cananea Mining District, yielded a crystallization age of 63.9 ± 1.3 Ma. Two Re-Os molybdenite ages yielded an identical age of 63.1 ± 0.4 Ma, Suggesting a restricted period of mineralization. Re-Os data indicate that mineralization in Cananea District, spanned ~4 m.y. in three discrete pulses at ~59 Ma, ~61 Ma and ~63Ma. El Arco porphyry copper deposit, Baja California, Mexico, yielded a Middle Jurassic crystallization age (U-Pb) of 164.7 ± 6.7 Ma and a Re-Os mineralization age of 164.1 ± 0.4 Ma and not ~100 Ma as previously determinated. Porphyry copper deposits in Mexico range in age from 164 Ma to 54 Ma and the mineralization in Sonora state occurred in two different periods, but magmatism overlaps in space and time.